1. Field of the Invention
The present invention relates to a semiconductor wafer and a method for cutting the same, and more particularly, to a semiconductor wafer and a method for cutting the same capable of separating the semiconductor wafer by natural cleavage planes.
2. Discussion of the Related Art
Generally, in dicing a semiconductor wafer into individual semiconductor chips, a dicing saw equipped with a diamond tip or a scriber have been used.
The dicing saw is a kind of cutting devices, which fully cuts the semiconductor wafer by rotating a disc-type blade equipped with a diamond tip or draws wide grooves corresponding to the width of the blade.
The scriber draws scribe lines having a fine width and a predetermined depth on a semiconductor wafer through a reciprocating motion of a leading end thereof equipped with a diamond tip.
When using the dicing saw, chipping or cracks are likely to occur at sectional surfaces and accuracy of the cutting is hardly guaranteed. Therefore, the scriber is more popularly used in the cutting process for fabricating the semiconductor chips.
However, even the scriber produces a quantity of pollutive materials during the cutting since it uses a mechanical driving system of the diamond tip. Moreover, the mechanical driving force may incur undesirable delamination of the semiconductor layer.
Such a problem occurs more seriously when cutting the semiconductor wafer for fabricating a blue light emitting diode (LED).
The semiconductor layer of the blue LED comprises gallium nitride (GaN)-based compounds including GaN, indium GaN (InGaN), and gallium aluminum nitride (GaAlN). Here, a sapphire substrate is generally used as a wafer for growth of a semiconductor crystal. However, since the sapphire substrate and the semiconductor layer containing the GaN-based compounds have different crystal properties from each other, delamination is apt to be generated.
In addition, the sapphire substrate and the semiconductor layer of the GaN-based compounds are very hard, having the Mohs hardness scale 9. Therefore, even with the diamond tip of the scriber, the cutting process takes a long time. More specifically, the cutting process occupies nearly 70% of the whole fabrication time.
Furthermore, in the sapphire substrate or the semiconductor layer of the GaN-based compounds, the semiconductor wafer may be cracked rather than being bent or separated along natural cleavage planes. Also, ridges of the semiconductor wafer may be damaged.
If the cracking or the damage of ridges occurs, the laser diode may not oscillate at all. Although the oscillation is performed, the laser property is greatly deteriorated.